Corsair, a leading provider of enthusiast-class PC components, on Friday published a list of power supply units (PSUs) compatible with the forthcoming Intel Core i-series “Haswell” microprocessors. Currently the company has over 20 PSUs that are guaranteed to be compatible with Intel Corp.’s next-gen chips and over 30 that are believed to support all the features of the new CPUs.

It recently transpired that Intel Haswell's C6/C7 power states require a minimum load of 0.05A on the 12V2 rail, whereas many desktop PSUs just cannot provide that low current. Numerous older PSUs, which comply with ATX12V v2.3 design guidelines that only called for a minimum load of 0.5A on the CPU power rail, can be equipped with a less sophisticated internal feedback loop/protection that cannot supply 0.05A to CPU. As a result, unless C6/C7 power states are disabled in the BIOS, PCs with older/cheap PSUs may become unstable when processors enter these states. To make the matters worse, many power supply units do not report minimum currents supported by 12V2 rail. As a result, it is now hard for system makers and end-users to determine whether their PSUs are Intel Core i-series “Haswell” compatible.

According to Corsair, the potential problem comes up when the CPU enters sleep mode, but there is still a substantial load on the power supply's non-primary rails (the +3.3V and +5V). If the load on these non-primary rails are above a certain threshold (which varies by PSU), the +12V can go out of spec (voltages greater than +12.6V). If the +12V is out of spec when the motherboard comes out of the sleep state, the PSU's protection may prevent the PSU from running and will cause the power supply to "latch off". This will require the user to cycle the power on their power supply using the power switch on the back of the unit.

While Corsair is still working with Intel on the details of the testing methodology the chipmaker uses to check PSUs for Haswell compatibility, it is already known that a power supply that uses DC to DC for the non-primary rails (the +3.3V and +5V) will not have an issue with the new low power sleep states. This is because a DC to DC buck converter is used to convert +12V to +3.3V and +5V. This means that no matter what load the CPU puts on the power supply, there will always be a load on the +12V because the +12V is required to provide power to +3.3V and +5V.

Corsair utilizes this DC to DC technology in most of its power supplies. Starting with the CX750 and CX750M and moving all of the way through the GS series, TX and TX-M series, the HX series, both the AX series Gold and AX series Platinum, and the new AXi Series. Basically, Corsair can provide a Haswell-compatible PSU at almost any budget.